First find the curve then area

Let $f\left( x \right)$ be a differentiable function such that

$f\left( x+y \right) ={ e }^{ x }f\left( y \right) +{ e }^{ y }f\left( x \right)$

for all $x,y$

And Given that $f^{ ' }\left( x \right) =1$

Find the Area bounded by the curve and x axis